## 1 Introduction  
Aripiprazole (ARP) is among the atypical neuroleptics used to treat mental illnesses, including schizophrenia [1]. In the case of oral drug formulations, low adherence is observed, which was the reason for the development of ARP long-acting injections (ALAlAs). Currently, there are only two medicinal products available that can be categorized as ALAIs, _i.e._, Ability Maintena(r) and Aristada(r). However, their administration has several major disadvantages, _e.g._, (i) the risk of pain at the injection site, (ii) no possibility of interrupting therapy, and (iii) the need to be administered on an outpatient basis [2, 3]. Another problem with ALAIs is the release profile with a lag phase after administration, which requires oral supplementation [4, 5].  
An attempt to solve the pointed problems of the current oral therapy and ALAIs involves parenteral nano- and microformulations based on poly(lactide), poly(lactide-_co_-glycolide) (PLGA), and poly(caprolactone) [6; 7; 8; 9]. Their formulation often requires the use of solvents, resulting in the following disadvantages: (i) a different loading efficiency for ARP depending on the composition of the polymer carrier (3.7-80.0%); (ii) different sizes of the formulation [6; 7; 8; 9]; (iii) the risk of changes in the crystalline form of ARP [10]; (iv) the need to eliminate the residual organic solvent [11]; and (v) the decrease in the molecular weight (\(M_{n}\)) of the polymers [12]. Rods formulated by hot melt extrusion (HME) are an alternative solution in the processing of thermoplastic polymers. They may largely eliminate the pointed disadvantages of nano- and microformulation. HME is characterized by: (i) the high loading efficiency of the drug substance, _e.g._, for poly(L-lactide-_co_-glycolide-_co_-trimethylene carbonate) rods with ARP it was \(\sim\)94% tested previously [13]; (ii) eliminating solvents [12; 14]; and (iii) the possibility of removing the formulation if side effects occur. However, HME should be also considered as the method of choice. Imparting fluidity to a thermoplastic polymer requires the use of elevated temperatures, which may cause a risk of thermal degradation of the drug substance and polymer carrier [12; 14].  
ARP exhibits crystalline polymorphism, including the pseudo-polymorphs and the amorphous form [10; 15]. For ALAI development using the HME method, crystalline polymorphism of ARP must be taken into account to ensure the bioavailability and stability of ARP. Previously, in the study of ARP structure by proton nuclear magnetic resonance (\({}^{1}\)H NMR) spectroscopy, the lack of influence of HME at 105 \({}^{\circ}\)C, _i.e._, below the melting point of ARP (135.0-148.5 \({}^{\circ}\)C according to measurements of [PERSON] and coworkers [16]) was determined [13].  
This study aimed to use HME to formulate rods with ARP based on thermoplastic terpolymers, _i.e._, poly(D,L-lactide-_co_-glycolide-_co_-trimethylene carbonate) with a \(M_{n}\) of 21 kDa (Td,L 21), poly(L-lactide-_co_-glycolide-_co_-trimethylene carbonate) with a \(M_{n}\) of 59 kDa (Tl 59), and with a \(M_{n}\) of 77 kDa (Tl 77). The study was carried out in several stages: (i) determination of the influence of HME conditions on the structural, thermal, and morphological properties of ARP; (ii) synthesis of Td,L 21, Tl 59, and Tl 77; (iii) rod formulation; and (iv) determination of the composition, thermal properties, and \(M_{n}\) of the terpolymers, the morphological features and mechanical properties of the rods, and (v) determination of the rate of hydrolytic degradation of rods.