A new method for the determination of a hydrosilanization inhibitor applied to measurements during curing of a silicone elastomer

A new method for the quantitative determination of the hydrosilylation inhibitor 1‐ethynyl‐1‐cyclohexanol in a poly(dimethyl siloxane) matrix is presented. The method is based on headspace gas chromatography directly from the semisolid sample without solvent addition. The method was found to be both selective and sensitive. The relative standard deviation of the method was estimated to be 6%. The semisolid silicone sample was weighed directly in a headspace autosampler vial. After sample equilibration at 90°C for 1 h, the gas phase was injected into a gas chromatography system with a nonpolar methyl silicone capillary column. The inhibitor was detected with a flame ionization detector. The standard addition procedure was used for quantification. Recovery data on the inhibitor from the silicone during curing suggests that the inhibitor reacts with the silicone hydride crosslinker in the presence of the platinum catalyst to become part of the polymer network. This implies that the inhibitor will not migrate out from the silicone elastomer, which is a great advantage particularly for silicone elastomers used for medical devices or controlled drug release applications. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2349–2353, 2001     

Fatigue-resistant silicone elastomer formulations

Fatigue-resistant elastomers have been prepared using various metal oxides as fillers in poly(dimethylsiloxane) (PDMS)-based elastomers. The judicious choice of inorganic fillers produced elastomers that were stable under cyclic testing at elevated temperatures. These experiments were carried out using the Mechanical Energy Resolver, an instrument modified to reduce testing time from approximately 6 weeks to 60 h. Four elastomers showed stable storage moduli, were creep resistant, and showed less than 1% weight loss after 60 h. By comparison, a formulation prepared with alumina as the filler showed high rates of creep and greater than 10% weight loss. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1633–1641, 1998     

Studies of cyclic and linear poly(dimethyl siloxanes):7. Diffusion behaviour in a poor solvent

The diffusion coefficients (D) of cyclic and linear poly(dimethylsiloxanes) (PDMS) have been measured in bromocyclohexane at 288 K and 301 K. Bromocyclohexane has previously been reported to be a θ-solvent for high molar mass linear PDMS at 301 K, but the hydrodynamic radii reported here apparently show the effects of molecular expansion at both temperatures. In addition, the hydrodynamic radii of both linear and cyclic PDMS are found to be insensitive to whether the solvent is toluene or bromocyclohexane. The ratio of friction coefficients $\text{f}{}_{\mathrm{r}}\text{f}{}_{\mathrm{l}}$ for the ring (r) and linear (l) molecules of the same number of segments (x) is in good agreement with the theoretical value of $\text{8}\text{3π}$ in the impermeable limit and with the experimental value found previously in toluene solution. As x decreases the ratio $\text{f}{}_{\mathrm{r}}\text{f}{}_{\mathrm{l}}$ tends to unity, illustrating the increasing importance of free-draining at low molar mass.     

Relationship between the composition of polycarbonate copolymers and the refractive index

With a polycarbonate (PC)–poly(methyl methacrylate) (PMMA) graft copolymer and a PC–poly(dimethyl siloxane) (PDMS) block copolymer, the relationship between the composition of PC copolymers and the refractive index (n_D) was investigated. According to the results, with a PMMA content of 38 wt %, the n_D value of the PC–PMMA graft copolymer was nearly the same as that of electrical (E) glass (n_D = 1.545), and with a PMMA content of 6 wt %, it was nearly the same as that of electrical corrosion resistance (ECR) glass (n_D = 1.579). However, with a PDMS content of 19 wt %, the n_D value of the PC–PDMS block copolymer was nearly the same as that of E glass, and with a PDMS content of 2 wt %, it was nearly the same as that of ECR glass. The combination of the PC–PDMS block copolymer and the glass fibers (GFs) of ECR glass led to haze values of 8 and 16% with GF contents of 10 and 20%, respectively. © 2002 John Wiley & Sons, Inc. J Appl Polym Sci 84: 514–521, 2002; DOI 10.1002/app.2355     

Studies of cyclic and linear poly(dimethyl siloxanes): 8. Light scattering measurements in good and poor solvents

Weight average molar masses (M_w) and second virial coefficients (A₂) have been measured for linear and cyclic poly(dimethyl siloxane) (PDMS) fractions in toluene at 298K and for linear PDMS in bromocyclohexane at 301K. The values of M_w are compared with those deduced previously using gel permeation chromatography, broadly confirming the values already assigned to the fractions. The values of A₂ for linear PDMS in toluene are shown to be consistent with previously published values for oligomeric linear PDMS. The values of A₂ for cyclic PDMS approach those of linear PDMS for M_w<～1000 g mol^?1 and decrease more rapidly as M_w increases in approximate agreement with theoretical predictions. In addition, the conventional relations between A₂ and the expansion factor α_s are shown to be inapplicable at low molar mass.     

Studies of cyclic and linear poly(dimethyl siloxanes): 9. Quasi-elastic light scattering and concentration dependences of diffusion coefficients

The concentration dependences of the diffusion coefficients (D) of linear and cyclic poly(dimethyl siloxanes) (PDMS) in toluene at 298K are reported. Three cyclic/linear pairs of fractions with molar masses in the range 300 to 23 500 g mol^?1 were used. The values of D obtained by quasielastic scattering were in good agreement with those measured by the classical boundary-spreading technique. Analysis of the concentration dependences in terms of the theory of Pyun and Fixman indicates that the solute molecules show a minimum of interpenetration in toluene at 298K.     

Synthesis and characterization of poly(dimethyl siloxane) containing poly(vinyl pyrrolidinone) block copolymers

ABA‐type block copolymers containing segments of poly(dimethyl siloxane) and poly(vinyl pyrrolidinone) were synthesized. Dihydroxyl‐terminated poly(dimethyl siloxane) was reacted with isophorone diisocyanate and then with t‐butyl hydroperoxide to obtain macroinitiators having siloxane units. The peroxidic diradical macroinitiators were used to polymerize vinyl pyrrolidinone monomer to synthesize ABA‐type block copolymers. By use of physicochemical methods, the structure was confirmed, and its characterization was accomplished. Mechanical and thermal characterizations of copolymers were made by stress–strain tests and differential scanning calorimetric measurements. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1915–1922, 1999     

Studies of cyclic and linear poly(dimethyl-siloxanes): 11. Shapes of ring and chain molecules

The equilibrium shapes of cyclic and linear poly(dimethyl siloxane) (PDMS) molecules have been investigated using Flory, Crescenzi and Mark's rotational isomeric state model, together with a Monte Carlo method described previously. The principal axes of the equivalent ellipsoids have been computed and the major change on ring formation was found to be a reduction in the longest axis of the ellipsoid. This result is in agreement with previous studies of other ring molecules. The shapes of the cyclics $\text{[(}\text{CH}{}_3\text{)}{}_2\text{SiO}\text{]}{}_{\mathrm{<mtext>w</mtext><mtext>2</mtext>}}$ in the region w=20 are disc-like and this observation is related to the different bond angles at silicon and oxygen atoms. Bulk densities and refractive indices of PDMS rings are discussed in relation to the calculated molecular shapes. Histograms are used to illustrate the proportional frequency functions of the radii of gyration and their components s_x, s_y and s_z.     

Studies of cyclic and linear poly(dimethyl siloxanes): 14. Particle scattering functions

Particle scattering functions P(Q) (where Q represents the wave vector), have been calculated using a Monte Carlo method for cyclic and linear poly(dimethyl siloxanes) (PDMS) containing up to 100 skeletal bonds. A maximum is found in the Kratky plot at $\text{u (=Q〈s}{}^2\text{〉}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{)≈2.0}$ for cyclic PDMS (with root-mean-square radii of gyration $\text{〈s}{}^2\text{〉}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$) and this is in satisfactory agreement with the analytical calculations of Casassa and of Burchard and Schmidt. In addition, other clearly-defined maxima are found at u≈5.0 for PDMS ring molecules with less than ≈40 skeletal atoms. These maxima are believed to be characteristic of small cyclic molecules as they are also predicted for small polymethylene rings. Comparisons are made with experimental small-angle neutron scattering (SANS) data for cyclic and linear PDMS. A single maximum in the experimental Kratky plot at u≈2.0 is found for PDMS ring molecules with an average of 550 skeletal atoms. The experimental data for cyclic PDMS are in better agreement with the Monte Carlo calculations of P(u) than with analytical predictions up to u≈2.0.     

双组分有机硅涂料及其对有机玻璃表面的增强作用

以正硅酸乙酯和甲基三甲氧基硅烷为主要原料,添加适量的γ-环氧丙氧丙基三甲氧基硅烷、γ-甲基丙烯酰氧丙基三甲氧基硅烷、流平剂、异丙醇,配成A组分;在一定量的盐酸水溶液中加入适量的固化剂作为B组分.将A、B组分按一定比例混合,在室温下放置4 h以上,即得耐磨涂料;并利用提拉法镀制在聚甲基丙烯酸甲酯镜片表面.研究了涂料的固化条件.结果表明,在80℃下固化3 h,得到厚度在3～5 μm的涂层,其铅笔硬度可达6 H,并可明显提高有机玻璃镜片表面的耐擦伤性能,在有机玻璃表面的脱落情况为0级,且有一定的增透作用.A、B组分在室温下的贮存期均为6个月.     

Studies of cyclic and linear poly(dimethyl siloxanes): 13. Static dielectric measurements and dipole moments

The static dielectric permittivities, refractive indices and densities of undiluted oligomeric cyclic and linear dimethyl siloxanes and narrow fractions of cyclic and linear poly(dimethyl siloxanes) have been measured for number-average molar masses M?_n in the range $\text{160 <}\text{M}\text{?}{}_{\mathrm{n}}\text{< 7700}$ at temperatures from 298 to 313 K. Measured total dielectric polarizations have been resolved into their electronic, atomic and orientation components and dipole moments have been derived. The dipole moments of cyclic oligomers ((CH₃)₂SiO)_x (for example, with x = 4, 5) are markedly lower than the dipole moments of the corresponding linear oligomers containing the same number of siloxane bonds. However, for x ? 10, the dipole moments of cyclic dimethyl siloxanes are identical, within experimental error, to those of the corresponding linear dimethyl siloxanes. Measured static dielectric permittivities of the dimethyl siloxanes and poly(dimethyl siloxanes) in solution in cyclohexane are markedly different from the corresponding values for the undiluted siloxanes. These differences are interpreted as resulting from the specific solvent effects.     

Studies of cyclic and linear poly(dimethyl siloxanes): 10. Calculations of radii of gyration

A Monte Carlo method has been devised for calculating the conformation-dependent properties of cyclic poly(dimethyl siloxanes) (PDMS), using Flory, Crescenzi and Mark's rotational isomeric state model. Calculated values of the mean-square radii of gyration 〈s²_r〉 of ring molecules unperturbed by excluded volume effects and containing 8–100 skeletal atoms are compared with the 〈s²_l〉 values for the corresponding unperturbed chain molecules. Exact enumeration methods were also employed for rings $\text{[(}\text{CH}{}_3\text{)}{}_2\text{SiO}\text{]}{}_{\mathrm{<mtext>w</mtext><mtext>2</mtext>}}$ with w ? 24 and the results found to be in close agreement with those obtained by the Monte Carlo method. The ratio $\text{〈s}{}^2{}_{\mathrm{l}}\text{〉}\text{〈s}{}^2{}_{\mathrm{r}}\text{〉}$ was found to attain limiting values close to 2.0 for w > 30, in agreement with theoretical predictions.     

Imparting antifouling properties of silicone hydrogels by grafting poly(ethylene glycol) methyl ether acrylate initiated by UV light

Both hydrophilic and antifouling surfaces were prepared on silicone hydrogels with poly(ethylene glycol) methyl ether acrylate (PEGMA) grafted by UV-induced radical polymerization. The PEGMA-grafted silicone hydrogels were characterized by graft yield and static water contact angle measurements. According to the results, the graft yield reached a maximum at 8 min of UV exposure time and 20 wt% PEGMA concentration. The modified silicone hydrogels possessed hydrophilic surfaces with the lowest water contact angle of 36°. The oxygen permeability and transparency of the PEGMA-grafted silicone hydrogels were as high as the unmodified silicone hydrogel. The mechanical property of silicone hydrogels was maintained at about 95% of the tensile strength and elastic modulus after the PEGMA grafting. The in vitro single protein adsorption on the PEGMA-grafted silicone hydrogels decreased by 70–80% compared to the unmodified silicone hydrogel. The PEGMA-grafted silicone hydrogel is expected to be a novel biomaterial, which possesses excellent surface hydrophilicity, antifouling property, oxygen permeability, and mechanical property. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Development of wear-resistant thermoplastic polyurethanes by blending with poly(dimethyl siloxane). II. A packing model

It has been shown in a previous article that melt blending of low levels of commercial poly(dimethyl siloxane) (PDMS) fluid with commercial thermoplastic polyurethanes has a significant positive impact on the coefficient of friction (CoF) and on the mechanical and wear properties of the polyurethanes. The improvements in CoF and wear resistance were expected due to surface modification of the polymer; however, the improvements in the mechanical properties were much more significant than expected. Evidence presented in the earlier publication suggests that the changes in the wear and mechanical properties are not due to surface modification alone, but are largely due to modification of the bulk by PDMS. In this article a model is presented that accounts for the observed relationship between PDMS content and the properties of the blends. It is proposed that the addition of PDMS facilitates an improved packing efficiency (antiplasticization) in the polyurethane soft domain, leading to improved material performance. Beyond an optimum PDMS concentration of 1.5–2.0%, phase separation of PDMS becomes significant, plasticization sets in, and mechanical properties then begin to diminish rapidly. This model has been rigorously investigated and has proven to be highly robust. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:939–950, 1997     

Studies of cyclic and linear poly(dimethyl siloxanes): 12. Observation of diffusion behaviour by quasielastic neutron scattering

High resolution neutron scattering experiments have been used to observe the diffusive motion of low molecular weight linear and cyclic poly(dimethyl siloxane) molecules in dilute solution in deuterated benzene. Diffusion coefficients (D) and hydrodynamic radii (R_H) have been compared with values obtained by light scattering for higher molecular weight samples and with radii of gyration (R_g) obtained by small-angle neutron scattering. While the ratio $\text{D}{}_{\mathrm{<mtext>ring</mtext>}}\text{D}{}_{\mathrm{<mtext>chain</mtext>}}$ is close to the predicted value of 0.85, the ratio $\text{R}{}_{\mathrm{g}}\text{R}{}_{\mathrm{<mtext>H</mtext>}}$ falls below the theoretical value for both ring and chain molecules. The scattering curves show effects arising from both centre of mass diffusion and internal molecular motion, and the observed inverse correlation times are compared with calculated behaviour as a function of scattering vector, Q.     

Strongly entangled polymer chains in a melt. Description of n.m.r. properties associated with a submolecule model

A model is proposed to illustrate properties of the transverse magnetic relaxation function, G(t), of proton pairs linked to strongly entangled polymer chains in a melt. According to this model, any polymer molecule is described as a freely jointed chain and it is divided into submolecules of equal contour length L^v_e. Every link is supposed to carry a proton pair; dipolar spin couplings between different proton pairs are neglected. The disentanglement relaxation time is supposed to be much longer than any characteristic time of the spin system; consequently, any submolecule observed on an n.m.r. time scale is supposed to have fixed ends. It is considered that the residual spin-coupling energy resulting from such a constraint governs the magnetic relaxation process. The free induction decay is expressed as a contour length function; its time evolution is shown to exhibit two ranges, which might be characterized by two relaxation times. The model is easily extended to rotating methyl groups. Theoretical results are compared with magnetic relaxation properties observed on entangled real chains: polydimethylsiloxane (PDMS) and cis-1,4-polybutadiene (PB). An attempt to adjust the contour length value to experimental results leads to the determination of average submolecule molecular weights M^v_e equal to 8200 and 2000 for PDMS and PB, respectively; the values usually obtained from viscoelastic plateau modulus measurements are 8100 and 1900, respectively.     

甲基氯硅烷生产过程中的污染防治对策

简述了国内有机硅市场状况，系统分析了甲基氯硅烷生产过程中污染物的产生环节、污染物的种类和数量，并据此提出了相应的污染防治措施。     

Synthesis and physical properties of poly(l‐lactic acid)‐poly(dimethyl siloxane) multiblock copolymers prepared by direct polycondensation

Multiblock copolymers consisting of poly(l ‐lactic acid) and poly(dimethyl siloxane) were prepared by the polycondensation of oligo(l ‐lactic acid) (OLLA) with dihydroxyl‐terminated oligo(dimethyl siloxane) and dicarboxyl‐terminated oligo(dimethyl siloxane). Copolymers with number‐average molecular weights of 18,000?33,000 Da and various content ratios of oligo(dimethyl siloxane) (ODMS) unit were obtained by changing the feed ratio of these oligomers. A film prepared from the copolymer with an ODMS content ratio of 0.37 exhibited two independent peaks at ?107°C and 37°C in the mechanical loss tangent for temperature dependence, suggesting the formation of microphase separation between the OLLA and ODMS segments. The film had a tensile strength of 3.2 MPa and a high elongation of 132%. The film also exhibited a high strain recovery even after repeated straining. The incorporation of dimethyl siloxane units as multiblock segments was confirmed to improve the flexibility of poly(l ‐lactic acid). © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40211.     

有机硅树脂合成及其共混改性研究

通过实验筛选出合成有机硅树脂的配方，讨论了原料配比、水解温度，介质酸度和溶剂组成对有机硅树脂的影响。采用傅里叶变换红外光谱表征了聚甲基丙烯酸丁酯(PBMA)共混改性有机硅树脂前后的结构特征；采用扫描电子显微镜分析了有机硅树脂、PBMA和PBMA共混改性有机硅树脂的微观结构，进而探讨，改性有机硅树脂室温同化机理，即有机硅树脂分子和PBMA分子之间的互相介入、互相贯穿使之形成网络，具有了自由基协同效应。     

聚1-丁烯热塑性弹性体的老化与防护

以拉伸性能为主要检测指标，考察了聚1-丁烯[P(1-Bt)]热塑性弹性体的热氧老化、紫外光老化和耐酸碱老化性能，制备了P(1-Bt)和三元乙丙胶(EPDM)防水卷材试样并进行对比：结果表明：单独使用抗氧剂1010，其用量在0．1～0．2质量份时具有较好的防热氧效果；1010与DLTP配合使用效果更佳，最佳配比为m(1010)：n(DLTP)=1：3(1010为0．2份)。热氧防老剂与紫外光吸收剂并用明显优于热氧防老剂或紫外光吸收剂单用时的防紫外光效果；ZnO对热氧老化和紫外光老化也具有很好的防护作用。P(1-Bt)制备的防水卷材的耐紫外光老化性能接近EPDM防水卷材，耐酸碱性能优于后者。