中文摘要：

以八甲基环四硅氧烷（D4）、苯基三（二甲基硅氧烷基）硅烷（PTDMS，俗称三氢封头剂）或四（二甲基硅氧基）硅烷（TDMS，俗称四氢封头剂）为原料，通过开环聚合法合成了三端氢基聚硅氧烷（PDMS—H3）和四端氢基聚硅氧烷（PDMS—H4）；再将其与甲基丙烯酸叔丁酯（t—BMA）在氯铂酸－四氢呋喃（THF）溶液催化下通过硅氢加成反应得到三端酯基聚硅氧烷（PDMS—t—BMA，）和四端酯基聚硅氧烷（PDMS—t－BMA。）；最后在浓硫酸催化下水解制得三端羧基聚硅氧烷（PDMS—COOH，）和四端羧基聚硅氧烷（PDMS—COOH4）。采用Fr—IR、^1H NMR和GPC对各阶段产物的结构和摩尔质量及其分布进行表征。结果表明，通过开环聚合、硅氢加成、酸性水解三步反应能够获得结构清晰、摩尔质量可控的多臂端羧基聚硅氧烷，且叔丁酯基聚硅氧烷酸性水解反应效率高，后处理简单，对硅氧烷主链的影响较小。

英文摘要：

With oetamethyleyclotetrasiloxane （ D4 ） , tris （dimethylsiloxy） phenylsilane （PTDMS） or tetrakis （dimethylsiloxy） -silane （TDMS） as raw materials, hydrogen terminated polydimethylsilox- anes （ PDMS-Hx, x = 3,4） were synthesized via ring-opening polymerization. Then tert-butyl methacry- late （t-BMA） was grafted to PDMS-Hx via hydrosilylation to prepare ester terminated polydimethylsilox- anes （PDMS-t-BMAx, x = 3,4） with H2PtC16 as catalyst, and the multi-branched carboxyl terminated polydimethylsiloxanes （PDMS-COOHx, x = 3,4） were prepared by subsequent hydrolysis reaction under acid. The structures and molecular weights of the products were characterized by FT-IR, ^1H NMR and GPC. Results show that multi-branched earboxyl terminated polydimethylsiloxanes with certain structures and molecular weights can be synthesized under control via a three-step procedure ： ring-opening polymeri- zation, hydrosilylation reaction and acid hydrolysis reaction. The acid hydrolysis of polydimethylsiloxanes with a tertiary-butyl ester group has advantages of high efficiency, simple after-treatment and less influence on siloxane backbone.