*1.3. Termination*

Terminating molecules in living AROP can serve several functions. At a minimum, they serve to quench the polymerization before redistribution processes associated with reversion, interchain back-biting, and interchain scrambling; their potential functions can be further divided into the following categories:

Non-functional termination;

Non-functional coupling to effect non-functional doubling of MW;

Non-functional coupling with block insertion;

Functional termination to form asymmetric macromers;

Functional coupling to form symmetric macromers;

Functional coupling to form branched structures.

Terminators in AROP processes are usually chlorosilanes, although other halosilanes and alkoxysilanes have been reported. Apart from the terminators found in the literature associated with living AROP of siloxanes, terminators normally associated with the living anionic polymerization of olefins and other organic polymers can provide similar termination for siloxanes [77,78].

#### *1.4. Macromers Commonly Reported in Literature*

The structures and properties listed in Table 3 are an aggregate of the most common siloxane macromers reported in the scholarly and commercial literature. They should not be considered exact values, but rather nominal values for similar materials. Similarly, heterobifunctional macromers are reported in Table 4.


#### **Table 3.** Commonly Reported Macromers.


**Table 3.** *Cont*.

**Asymmetric Monofunctional Siloxanes Code \* Description Molecular Weight, Mn Viscosity, cSt Density Refractive Index Reference** MCR-V21 MonoVINYL TERMINATED POLYDIMETHYLSILOXANE 5500–6500 80–120 0.97 1.403 [79,91,111] MCR-V25 MonoVINYL TERMINATED POLYDIMETHYLSILOXANE 15,000–20,000 400–600 0.97 1.403 [79] MCR-V41 MonoVINYL TERMINATED POLYDIMETHYLSILOXANE 55,000–65,000 8000–12,000 0.98 1.404 [79] MCR-XT11 MonoTRIETHOXYSILYLETHYL TERMINATED POLYDIMETHYLSILOXANE 500–1000 16–24 0.97 1.412 [79] **Symmetric Monofunctional Siloxanes** MCS-C13 MonoCARBINOL FUNCTIONAL POLYDIMETHYLSILOXANE, symmetric 550–650 35–40 1.02 1.446 [79]

**Table 3.** *Cont*.

**Asymmetric Monofunctional Siloxanes Code \* Description Molecular Weight, Mn Viscosity, cSt Density Refractive Index Reference** MCS-E15 Mono(2,3-EPOXY)PROPYL ETHER FUNCTIONAL POLYDIMETHYLSILOXANE, symmetric 800–900 45–55 1.09 1.398 [59,70,79] MCS-M11 MonoMETHACRYLOXYPROPYL FUNCTIONAL POLYDIMETHYLSILOXANE, symmetric 800–1000 7–9 0.93 1.417 [59,60,70,79,93] MCS-MXt11 MonoMETHACRYLOXYPROPYL FUNCTIONAL POLYDIMETHYLSILOXANE, METHOXYPROPYL TERMINATED, symmetric 900–1100 8–12 0.96 1.43 [60,79]

**Table 3.** *Cont*.

 **Asymmetric Monofunctional Siloxanes Code \* Description Molecular Weight, Mn Viscosity, cSt Density Refractive Index Reference** MCS-V212 MonoVINYL TERMINATED POLYDIMETHYLSILOXANE, symmetric 1200–1400 16–24 0.97 1.419 [79] 6L 2 6L 2 6L Q Q 2 2 2 2 MCS-VF14 monoVINYL FUNCTIONAL POLYDIMETHYLSILOXANE, TETRAHYDROFURFURY-LOXYPROPYL TERMINATED—symmetric 1000–1200 30–40 0.976 1.4141 [61,79,87,112] MCS-VXt15 MonoVINYL FUNCTIONAL POLYDIMETHYLSILOXANE, METHOXY(DIETHYLENEOXIDE) PROPYL TERMINATED, symmetric 1000–1200 40–60 0.96 1.42 [61,79,87,112] \* In order to provide a concise description of the macromer systems discussed, the following designation system was adopted: the first

two letters, MC, indicate macromer M structure with a C conventional dimethylsiloxane repeat unit; the third letter indicates whether it is asymmetric (R), symmetric (S), or T-structure (T). Macromer functionality and viscosity are indicated after a hyphen, as follows: (1) letters indicate functionality, where M is methacrylate, H is hydride, C is carbinol, V is vinyl, and E is methoxy; (2) numbers are the viscosity ranges of the macromer in powers of 10, followed by the first significant figure. For example, MCR-H25 indicates a macromer, an asymmetric architecture with hydride functionality, and a viscosity of 10<sup>2</sup> × 5 or 500 cSt. These designations provide a facile method of discussing comparative structures but are not intended to be detailed structural descriptions of the polymers. To remove ambiguity for ethyleneoxy designated X spacer groups, the lower-case letter t, for "tipped", or e, for "embedded", is used.


**Table3.***Cont*.

