## 1 Introduction  
Polycarbosilanes (PCS) gained considerable attention in the last two decades, due to their interesting optoelectronic and heat-resistant applications, but most important are applications as oxygen-free ceramic precursors [1; 2; 3; 4; 5]. Recently, ordered mesoporous non-oxide materials [6], silicon carbide fibers [7] and ceramic foams [8] could be obtained by the so-called polymer precursor route of PCS and metal-substituted PCS derivatives after pyrolysis [9]. There are various synthetic routes for controlling the PCS structure, which is unambiguously important for pursued ceramic materials with sufficient ceramic yields. Strategies range from Kumada rearrangement of silanes [10], Grignard coupling [11; 12; 13] to Pt(0)-catalyzed ring opening polymerization (ROP) of cyclic carbosilanes [9; 14]. The latter method has the advantage that well-defined hyperbranched materials can be obtained with high ceramic yields after pyrolysis. A postmodification of more intensively investigated polymers, e.g., polyisoprene or poly(ethylene oxide) (PEO) and also unsaturated PCS via hydrosilylation is a feasible strategy to introduce pendant side groups with additional functionalities [15; 16; 17; 18; 19; 20]. The above mentioned synthetic strategies suffer from the disadvantages that well-defined PCS with respect to narrowly distributed high molar masses cannot be obtained, as well as it is impossible to gain block copolymer structures. Amongst all synthetic protocols, anionic polymerization--especially anionic ROP--has several advantages and enables one to synthesize various block copolymers (BC) with precise control over block compositions, a well-defined constitution and narrowly distributed molar masses. Fascinating microstructures for manifold applications are accessible via self-assembly of such polymers [21]. For example, well-defined BCs consisting of polyisoprene and polymers with laterally bonded alkyl-silane groups were recently prepared by sequential anionic polymerization and have been used as membranes for gas separation applications [22]. The anionic ring opening polymerization (ROP) of ring-strained cyclic silanes, carbosilanes and metal-containing carbosilanes has also been reported and lead to well-defined polymers [23; 24; 25; 26; 27; 28; 29; 30; 31; 32]. Out of all cyclic carbosilanes, 1,1-dimethylsilacyclobutane (DMSB) is a well-known monomer, due to its convenient chemical and also commercial availability. The anionic ROP of DMSB leads to constitutional well-defined crystallizable polymers. Furthermore, it is reported that polymerization in a polar solvent, such as tetrahydrofuran (THF), at low temperature forces results in poly(1,1-dimethylsilacyclobutane) (PDMSB) chains precipitating during the polymerization and, hence, a loss of the \"living\" nature of the chains occurs, hampering the possibility of BC formation [33; 34]. In spite of those obstacles, PDMSB-containing block copolymers with polystyrene (PS) have been synthesized by [PERSON] _et al._ using a slightly modified synthetic protocol [35]. Fascinating BC structures with PS have been obtained after BC self-assembly, and even after subsequent pyrolysis, highly-ordered ceramic structures could be maintained. The synthesis and microphase separation of BCs consisting of PDMSB and various ferrocene-containing polymers have also been reported [36]. In the present study, we firstly synthesize and investigate PDMSB homopolymers obtained by anionic ROP, and results are compared to previously reported studies. Absolute molar masses, which are determined via multi-angle laser light scattering size exclusion chromatography (SEC-MALLS) measurements, are varied in the range of 2.3 kg mol\({}^{-1}\) to 60 kg mol\({}^{-1}\), with low polydispersities for every sample (polydispersity index (PDI) values range from 1.04 to 1.15). The thermal behavior of PDMSB is reinvestigated by differential scanning calorimetry (DSC) measurements revealing two melting peaks, but only one crystallization peak for PDMSB chains with low molar masses.