Syntheses and properties of UV-autocurable prepolymers. Semicrystalline urethane-multiacrylates

A series of UV-autocurable urethane-multiacrylate prepolymers, which were semicrystalline and showed melting points in the region of 40–50°C, was synthesized. Also, the effects of curing temperature and acrylic functionality on the structure and properties of the cured films were investigated. These prepolymers are solids and opaque at room temperature. In general, UV curing reactions of solid prepolymers are less efficient when compared with those of liquid prepolymers. UV curing reactions at curing temperatures below the melting point (T_m) of the prepolymers produced semicrystalline urethane-multiacrylate cured films. On the contrary, UV curing reactions above T_m destroyed the crystalline phase of the prepolymers and improved the transparency of the cured films. The films cured below T_m of the prepolymers had higher both breaking strength and Young's modulus, and a higher glass transition temperature (T_g), but a lower elongation at break than those cured above T_m. Such curing temperature effects were attributed to the retention or disappearance of the crystalline structure of the prepolymers during UV curing reaction. At curing temperatures below T_m, an increase in acrylic functionality of the prepolymer resulted in a fast curing rate and a higher crosslinking density of the cured films. Therefore, an increase in acrylic functionality of the prepolymers gave cured films with higher breaking strength and Young's modulus, but a lower elongation at break.     

Synthesis of polymer materials by low energy electron beam. I. Polyurethane–acrylate materials prepared by the EB and the UV solid-state polymerization

Structure and properties of films obtained by the electron beam (EB) and the ultraviolet light (UV) solid-state polymerization of polyurethane–acrylate prepolymer were examined to reveal the characteristics of these radiation polymerizations. The prepolymer was synthesized by the reaction of poly(butylene adipate)diol, 4,4′-diphenylmethane diisocyanate, and 2-hydroxyethyl acrylate. EB polymerization behaviors of the prepolymer produced a unique polymer film different from that obtained by UV irradiation. Although polyurethane–acrylate films from the EB and the UV solid-state polymerizations consisted mainly of amorphous and crystalline phases, it was proved that the film from 10 Mrad of EB irradiation at 25°C had higher crystallinity and larger crystallite size than the film from UV irradiation. This is assumed to be due to the reason that EB irradiation below the melting point of the polyurethane–acrylate can lead to crosslinking without the destruction of the original crystalline structure. On the other hand, the UV polymerization proceeded with the melting of the crystalline structure by absorbing other lights than the UV absorbed by a photoinitiator. The EB-polymerized film which was crosslinked more densely than the UV-polymerized film showed higher mechanical strength than the latter film.     

Structure variation and puncture resistance of stretched crosslinked polyethylene film: Effects of stretching temperature

Crosslinked polyethylene films were prepared and stretched at different temperatures (below and above melting temperature). The stretching temperature exhibited pronounced effects on the structure and puncture resistance of the films. Combining the results of differential scanning calorimetry, 1D X-ray diffraction, 2D X-ray diffraction, and scanning electron microscope, it was demonstrated that the film stretched above T _m has lower crystallinity, thinner lamellar, and larger crystal grain size than that stretched below but near T _m. All the stretched films showed highly oriented lamellae in the bulk and arranged perpendicular to the stretching direction. The crystals of the film stretched below T _m were arranged in highly aligned microfibrils with distinct interlamellar boundary and the crystals of the film stretched above T _m were arranged in a progressively less orderly manner with increased interlamellar entanglement. Due to this structure difference, the puncture resistances of the films stretched above T _m were much larger than that stretched below T _m. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47542.     

Influence of Codiluent on the Properties of Radiation-Cured Films

A number of formulations were developed using urethane diacrylate oligomer in combination with a series of monofunctional and multifunctional reactive diluents possessing diverse glass transition temperatures from ?50°C to 250°C. Films prepared with these formulations were cured under ultraviolet (UV) radiation; their properties, such as hardness, gel content, tensile characteristics, etc., were determined and compared with those of the films cured by electron beam (EB) radiation. Effect of comonomer diluents was investigated in these cases. A good correlation was observed between these properties and the glass transition temperature (T _g) of the copolymer (cured film), prepared under radiation with urethane acrylate, monomer, and comonomer.     

Poly(L‐Lactide), 8. High‐Temperature Hydrolysis of Poly(L‐Lactide) Films with Different Crystallinities and Crystalline Thicknesses in Phosphate‐Buffered Solution

Poly(L ‐lactide) (PLLA) films having different crystallinities (X_c's) and crystalline thicknesses (L_c's) were prepared by annealing at different temperatures (T_a's) from the melt and their high‐temperature hydrolysis was investigated at 97°C in phosphate‐buffered solution. The changes in remaining weight, molecular weight distribution, and surface morphology of the PLLA films during hydrolysis revealed that their hydrolysis at the high temperature in phosphate‐buffered solution proceeds homogeneously along the film cross‐section mainly via the bulk erosion mechanism and that the hydrolysis takes place predominantly and randomly at the chains in the amorphous region. The remaining weight was higher for the PLLA films having high initial X_c when compared at the same hydrolysis time above 30 h. However, the difference in the hydrolysis rate between the initially amorphous and crystallized PLLA films at 97°C was smaller than that at 37°C, due to rapid crystallization of the initially amorphous PLLA film by exposure to crystallizable high temperature in phosphate‐buffered solution. The hydrolysis constant (k) values of the films at 97°C for the period of 0–8 h, 0.059–0.085 h^–1 (1.4–2.0 d^–1), were three orders of magnitude higher than those at 37°C for the period of 0–12 months, 2.2–3.4×10^–3 d^–1. The melting temperature (T_m) and X_c of the PLLA films decreased and increased, respectively, monotonously with hydrolysis time, excluding the initial increase in T_m for the PLLA films prepared at T_a = 100, 120, and 140°C in the first 8, 16, and 16 h, respectively. A specific peak that appeared at a low molecular weight around 1×10⁴ in the GPC spectra was ascribed to the component of one fold in the crystalline region. The relationship between T_m and L_c was found to be T_m (K) = 467·[1–1.61/L_c (nm)] for the PLLA films hydrolyzed at 97°C for 40 h.     

Synthesis and characterization of polyamide resins from soy-based dimer acids and different amides

A series of soy-based polyamides with different dimer acids and diamines were synthesized using a condensation polymerization technique. The molecular weight of polyamides prepared from 1,4-phenylenediamine increases greatly with a reaction temperature above 260°C. The physical properties of the polyamides, such as glass transition temperature (T_g), melting point (T_m), decomposition temperature (T_d), crystalline behavior, and mechanical strength strongly depend on their molecular weight and flexibility of diamines used. The aromatic-based polyamides have a higher T_g, T_m, T_d, and stronger mechanical strength than that of aliphatic-based polyamides. X-ray diffraction patterns of the samples indicate that all of the resins synthesized present a typical semicrystalline morphology. Polyamides made from hydrogenated dimer acid possess lower T_g and higher mechanical strength, compared with polyamides from unsaturated dimer acid with different dimer and trimer ratios. These results are analyzed and discussed in accordance with the influence of rigid aromatic segments and the microstructure of different dimer acids. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:305–314, 1998     

Production of biodegradable polyesters via enzymatic polymerization and solid state finishing

The synthesis of aliphatic polyesters (PEs) derived from diols (1,4‐butanediol and 1,8‐octanediol) and diacids or their derivatives (diethyl succinate, sebacic acid, 1,12‐dodecanedioic acid, and 1,14‐tetradecanedioic acid) was achieved in order to produce poly(butylene succinate) (PE 4.4), poly(octylene sebacate) (PE 8.10), poly(octylene dodecanate) (PE 8.12), and poly(octylene tetradecanate) (PE 8.14). The herein suggested procedure involved two stages, both sustainable and in accordance with the principles of “green” polymerization. The first comprised an enzymatic prepolymerization under vacuum, in the presence of diphenylether as solvent using Candida antarctica lipase B as biocatalyst, whereas a low‐temperature postpolymerization step [solid state polymerization (SSP)] followed in order to upgrade the PEs quality. In the enzymatically synthesized prepolymers, the range of number–average molecular weight attained was from 3700 to 8000 g/mol with yields reaching even 97%. Subsequently, SSP of PE 4.4 and 8.12 took place under vacuum or flowing nitrogen and lasted 10–48 h, at temperatures close to the prepolymer melting point (T_m ? T_SSP varied between 4°C and 14°C). The solid state finishing led to increase in the molecular weight depending on the prepolymer type, and it also contributed to improvement of the physical characteristics and the thermal properties of the enzymatically synthesized PEs. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40820.     

Morphology and texture development of uniaxially stretched poly(ethylene naphthalene‐2,6‐dicarboxylate)

The texture development of PEN films with different semicrystalline morphologies have been studied by X‐ray diffraction. These different structures have been obtained by uniaxially stretching PEN amorphous films at 100 and 160°C (below and above T_g) at different drawing ratios. Samples have also been characterized by DSC to determine the crystallinity ratios, the crystallization, and melting temperatures. To define the orientation of crystallites in the oriented samples, pole figures have been constructed, as a function of temperature and drawing ratio (DR) in the range 1.5–4. In the range from DR = 2 to 4 the orientation is clearly uniplanar‐axial. At T_draw = 100°C the crystallinity shown by DSC analysis is higher than the sample stretched at 160°C. The orientation is also higher when samples are stretched at 100°C. The naphthalene rings mainly stay in the plane of the film with a lower fraction perpendicular to the plane of the film. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 395–401, 2007     

Heat sealing of semicrystalline polymer films. II. Effect of melting distribution on heat-sealing behavior of polyolefins

Heat sealing of films, i. e., formation of a joint between two films by placing them fleetingly between heated platens, was experimentally investigated for a variety of semicrystalline polyolefins, especially various polyethlenes, to determine how sealing temperature affected seal strength measured at room temperature. Seal strength as a function of sealing temperature, SS(T), is closely related to the melting distribution of the polymer determined by DSC measurements, i. e., to the fraction of amorphous phase as a function of temperature, f_a(T). Seal initiation temperature, the temperature at which a specific, low level of seal strength of polyethylene films is achieved, corresponds to the temperature at which the fraction of amorphous phase equals 77±3%. At higher temperatures, SS(T) increases approximately as f_a(T) increases. At the final melting point of the polymer, i.e., when f_a(T) =1, seal strength reaches an approximately constant value termed the plateau seal strength. The magnitude of the plateau seal strength is determined by the yield stress of the polymer film. Thus, the heat-sealing curve, SS(T), for a polyethylene can be semiquantitatively predicted from the melting distribution and yield stress of the polymer. © 1994 John Wiley & Sons, Inc.     

Tuning the Properties of Shape-Memory Polyurethanes via the Nature of the Polyester Switching Segment

Shape-memory polymers that contain semicrystalline domains with a melting temperature (T_m) above and a crystallization temperature (T_c) below physiological temperature as fixing elements are useful to create medical devices or implants that can be custom-shaped inside or around the body. With the goal to expand the palette of materials that exhibit such properties, a series of segmented polyurethanes (PUs) containing different crystallizable polyester segments is investigated. The nature of the polyester, its molecular weight, and the ratio of hard to soft segments are systematically varied and the effect on the mechanical, thermal, and shape-memory properties of the various PUs is studied. Poly(1,12-dodecylene dodecanoate), poly(1,6-hexylene dodecanoate), and poly(ethylene sebacate) (PES) are selected as crystallizable polyester segments. The PES-based PUs display T_c values of 25–35 °C and a T_m of 60–63 °C, and allow good shape fixing at 37 °C.     

Preparation and properties of UV-autocurable BTDA-based epoxy-multiacrylate resins. Effects of the degree of polymerization and the epoxy type

A series of UV-autocurable epoxy-multiacrylate resins was synthesized, and the effects of degree of polymerization (DP) and epoxy type on their properties were investigated. These autocurable multiacrylate resins possess good pot life and are cured rapidly when exposed to ultraviolet (UV) without the addition of photoinitiator or photosensitizer. The curing rate of the autocurable resins was probably dependent on the number of abstractable hydrogen in epoxy resins. Stress-strain, differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA) were used to characterize the properties of cured multiacrylate resins. Increased crosslinking density of cured films improved tensile properties. Increasing the molar ratio of epoxy resin in the multiacrylate resins was found to decrease the effective acrylate concentration of resins and to depress crosslinking density of cured resins, which also resulted in an increased elongation at break but a decreased Young's modulus and breaking strength. Furthermore, the different structures of epoxy resins were used to give wide range properties of cured epoxy-multiacrylate resins with a glass transition temperature (T_g range from 74 to 102°C. The film properties of the multiacrylate resins coated on steel plates were also investigated.     

Synthesis of ethylene dichloride-based polysulfide polymers: investigation of polymerization yield and effect of sulfur content on solubility and flexibility

In this work, a series of polysulfide polymers were synthesized using organic monomer (ethylene dichloride) and sodium-based aqueous monomers via interfacial polymerization. The structural characteristics of aqueous monomers and synthesized polysulfide polymers were identified by Fourier transform infrared (FT-IR), Raman, and ultraviolet–visible-near infrared (UV–VIS-NIR) spectroscopies. The Optimum temperature of polymerization was obtained at 75°C. Benzyltriethylammonium chloride (BTEACl) and tetrabutylammonium bromide (TBAB) were used as phase transfer catalysts (PTC) where BTEACl showed better performance regarding the polymerization yield. Moreover, adding ethanol to polymerization media increased the polymerization yield significantly. The results showed that along with increasing sulfur in the structure of polymers, solubility and flexibility were increased whereas it decreased the hardness, melting point (T_m ) and glass transition temperature (T_g ) of obtained polymers.     

Curing and Thermal Properties of PEPEB Liquid Crystalline Diepoxide/Aromatic Diamine

The liquid crystalline epoxy resin p-phenylene di[4-2-(2,3-epoxypropyl)ethoxy] benzoate (PEPEB) was synthesized. The curing behavior of the liquid crystalline epoxy resin (LCER) with 4,4-diaminodiphenylmethane (DDM) was studied by fourier transform infrared (FTIR), differential scanning calorimetry (DSC), and torsional braid analysis (TBA). Morphology of curing product was observed by polarized optical microscopy (POM) at different temperatures. Nonisothermal curing kinetics of this system were investigated by DSC. Results show that the PEPEB has a smectic liquid crystalline structure, and the melting point, T _m, is 119°C, the clearing point is 184°C. The cured-system's gel point, T _I , is 83.5°C; cure temperature, T _P , is 111.6°C; and the disposal temperature, T _f , is 145.8°C; activation energy of curing reaction is 4.84 KJ/mol. Observation by POM shows that with the upgrade of initial curing temperature, the filament structure of this system transferred from anisotropy to isotropy.     

Properties of syndiotactic-rich poly(vinyl alcohol) thin film in water. V. Effect of initial temperature of heating on elongation

The effect of the initial temperature of heating on the elongation of syndiotactic-rich poly(vinyl alcohol) thin films was investigated in water under a load. The elongation ratios E_i after 4 h at fixed temperatures increased roughly with an increase in the initial temperature T_i and a decrease in the annealing temperature. E_i after 4 h was the smallest at T_i = 45°C for the films annealed at temperatures below 100°C. E_i was 6.8 at T_i = 60°C for the unannealed film and 1.12 at T_i = 70°C for the film annealed at 200°C. The elongation at break decreased and the temperature at break increased with an increase in annealing temperature, but those at the annealing temperature of 100°C were the smallest. The films annealed at 200°C did not break even at 98°C (boiling temperature) in water and the elongation ratio was 1.42–1.97 in the initial temperature range of 10–70°C. From these results, the relation between the elongation in water and the state of polymer chains in film was discussed.     

Oxygen barrier and enthalpy of melting of multilayer EVOH films after pressure‐assisted thermal processing and during storage

Pressure‐assisted thermal processing (PATP) is an advanced thermal process involving application of elevated pressures above 600 MPa on a preheated food for a holding time of 3 to 5 min, causing the volumetric temperature of food to increase above 100°C, to inactivate bacterial spores and enzymes. This study evaluated the influence of PATP on two state‐of‐the‐art multilayer EVOH films. Flexible pouches containing water as the food simulant were made from the two films and processed at 680 MPa for 3 min at 105°C and 680 MPa for 5 min at 100°C. Each film was investigated for its oxygen transmission rates (OTRs), melting temperature (T_m), enthalpy of melting (ΔH), and overall crystallinity before (control) and after processing. The changes in OTRs and total ΔH of the two films were also analyzed during a storage period of 240 days in ambient conditions after processing. Results showed a significant (P < 0.05) increase in the OTRs of the two films after PATP. However, PATP did not cause a significant (P > 0.05) change in the T_m and ΔH of the two films. The overall crystallinity of film A decreased, but improved slightly for film B after PATP. A recovery in the OTRs of the two films occurred during storage. The films also showed changes in the total ΔH measured during the storage period, which was used to explain the changes in the oxygen barrier properties. The OTR of both films remained below 2 cc/m² day, which is required in packaging applications for shelf‐stable foods with a 1‐year shelf life. This work demonstrates the advantages of using multilayer films containing EVOH as the barrier layer in PATP applications to produce shelf‐stable foods. This work also highlights the advantage of, DSC analysis for studying the physical ageing of polymers during storage. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Chain‐linked lactic acid polymers by benzene diisocyanate

Chain‐linked lactic acid polymers with high molecular weight were synthesized by two‐step polymerization method, including polycondensation and chain extending reactions. The effects of chain extender toluene diisocyanate (TDI) on the chain‐linked lactic acid polymers were studied. The polymers obtained were characterized by gel permeation chromatography, fourier transform infrared spectroscopy, ¹H NMR, and differential scanning calorimeter. Reactions between 1,4‐butanediol and lactic acid oligomers led to hydroxyl‐terminated prepolymer, which provided significant increase of molecular weight in the chain extending reaction. In addition, the glass transition temperature (T_g) and the melting temperature (T_m) were increased. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1045–1049, 2006     

Morphology–property relationship in oriented PET films: Microstructural reorganization during heat treatment

Morphology–property relationships for simultaneously biaxially stretched films and heatset with fixed dimensions in the temperature range of 100–240°C have been studied. The observed transition in various properties at 180°C can be explained on the basis of microstructural changes caused by competition among several processes, such as crystallization, solid-state thickening, melting, and molecular relaxation as well as by melting and recrystallization. The resulting structures and, thereby, the properties are different in temperature Regime-II (T_g to T_max) and Regime-III (T_max to T_m). In Regime-II, the high rate of crystallization compared to the rate of molecular relaxation develops a constrained amorphous phase, whereas the predominant melting and recrystallization process in Regime-III generates the relaxed amorphous phase. The structural reorganization during heat treatment is almost the same for uniaxially oriented film, fibers, and biaxially oriented films prepared under similar processing conditions. © 1994 John Wiley & Sons, Inc.     

Effects of reaction and cure temperatures on morphology and properties of poly(ester‐urethane)

Poly(ester‐urethane) was synthesized from poly(ethylene glycol adipate) (PEG) and 2,4‐toluene diisocyanate (TDI) to study the effects of reaction temperature and cure temperature on the crystallization behavior, morphology, and mechanical properties of the semicrystalline polyurethane (PU). PEG as soft segment was first reacted with TDI as hard segment at 90, 100, and 110°C, respectively, to obtain three kinds of PU prepolymers, coded as PEPU‐90, PEPU‐100, and PEPU‐110. Then the PU prepolymers were crosslinked by 1,1,1‐tris (hydroxylmethyl) propane (TMP) and were cured at 18, 25, 40, 60, and 80°C. Their structure and properties were characterized by attenuated total reflection Fourier transform infrared, wide‐angle X‐ray diffraction, scanning electron microscopy, dynamic mechanical analysis, and tensile testing. With an increase of the reaction temperature from 90 to 100°C, the crystallinity degree of soft segment decreased, but interaction between soft and hard segments enhanced, leading to the increase of the glass transition temperature (T_g) of soft domain and tensile strength. When the cure temperature was above 60°C, miscibility between soft and hard segments of the PEPU films was improved, resulting in relatively low crystallinity and elongation at break, but high soft segment T_g and tensile strength. On the whole, all of the PEPU‐90, PEPU‐100, and PEPU‐110 films cured above 60°C possessed higher tensile strength and elongation at break than that of the films cured at other temperatures. The results revealed that the reaction temperature and cure temperature play an important role in the improvement of the crosslinking structure and mechanical properties of the semicrystalline PU. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 708–714, 2006     

Isothermal crystallization behavior of metallocene‐catalyzed isotactic polypropylene

Isothermal crystallization behavior of isotactic polypropylene (iPP) synthesized using metallocene catalyst was investigated in this work. The isotacticity of the polypropylene was characterized by ¹³C‐NMR spectroscopy. It was found that the melting temperature (T_m) of the iPP is 123.51°C and the crystallization temperature (T_c) is 93°C. The iPP synthesized in this work did not show a general increase of T_m with an increase of crystallization temperature T_c, due to the short crystallization time of 20 min and low molecular weight (number average molecular weight = 6,300). The iPP showed a tendency of increasing heat of fusion (ΔH_f) with decreasing crystallization temperature. All the spherulites of iPP samples showed negative birefringence. For the iPP sample crystallized at the highest T_c (= 123°C, just below T_m), the spherulite showed a pronounced Maltese Cross and a continuous sheaf‐like texture aligning radially, which suggests that R‐lamellaes are dominant in this spherulite. The crystalline structure of the iPP was also investigated by X‐ray diffraction. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 231–237, 2005     

Syntheses of cyclic poly(lactones) by zwitterionic ring opening polymerization catalyzed by N‐heterocyclic carbene

Synthesis of cyclic biopolymers from renewable monomers remains a big challenge because of lack of efficient catalysts. The organocatalyst of N‐heterocyclic carbene (NHC), (+)‐1‐methyl‐3‐menthoxymethyl imidazol‐2‐ylidene, is used to prepare cyclic polylactones including poly(ε‐caprolactone) (poly(ε‐CL)), poly(δ‐valearolactone) (poly(δ‐VL)), and poly(ε‐caprolactone‐co‐δ‐valearolactone) (poly(ε‐CL‐co‐δ‐VL)) via zwitterionic ring opening polymerization. The NHC catalyst is founded a highly efficient organic catalyst for the polymerization. The resulting cyclic polymers show a melting temperature (T_m) in a range of 20–60°C, which is dramatically lower than the T_m of cyclic poly(lactide) (T_m = 120–150°C). The resulting copolymer, cyclic poly(ε‐CL‐co‐δ‐VL) owns high molecular weight comparing with corresponding linear poly(ε‐CL‐co‐δ‐VL) produced by other catalysts. The synthesized cyclic homo and copolymers were characterized by ¹H‐, ¹³C‐NMR spectroscopy, gel permeation chromatography, differential scanning calorimetry–thermogravimetric analysis and matrix‐assisted laser desorption ionization‐time of flight mass spectrometry. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013